U.S. patent application number 10/087992 was filed with the patent office on 2002-10-31 for furnace and a method of controlling a furnace.
Invention is credited to McComb, Frederick Stephen, Morris, David John.
Application Number | 20020157582 10/087992 |
Document ID | / |
Family ID | 25589086 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020157582 |
Kind Code |
A1 |
McComb, Frederick Stephen ;
et al. |
October 31, 2002 |
Furnace and a method of controlling a furnace
Abstract
The invention provides a furnace having a frozen lining
inbetween a furnace lining and a furnace charge, the furnace having
means to control the operation of the furnace, including means to
measure the temperature in a wall of the furnace adjacent the
frozen lining, and to estimate the thickness of the frozen lining
as a function of the temperature in the wall, and means to control
the rate of heat production in the furnace to urge a thickness of
the frozen lining towards a predetermined value. Variables
including side wall thermocouple measurements, gas plant instrument
measurements, cooling system measurements and electrical, in-feed
and chemical composition recordings are monitored, analysed and
manipulated. There is also provided means to estimate a future
furnace charge composition, perform chemistry control, estimate a
material balance of the furnace, and perform inventory control over
the furnace.
Inventors: |
McComb, Frederick Stephen;
(Saldanha, ZA) ; Morris, David John; (Bedfordview,
ZA) |
Correspondence
Address: |
PENNIE & EDMONDS LLP
1667 K STREET NW
SUITE 1000
WASHINGTON
DC
20006
|
Family ID: |
25589086 |
Appl. No.: |
10/087992 |
Filed: |
March 5, 2002 |
Current U.S.
Class: |
110/185 ;
110/263; 110/336 |
Current CPC
Class: |
C21C 5/44 20130101; C21C
5/5264 20130101; C22B 34/1281 20130101; Y02P 10/20 20151101; Y02P
10/216 20151101 |
Class at
Publication: |
110/185 ;
110/263; 110/336 |
International
Class: |
F23N 005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 5, 2001 |
ZA |
2001/1817 |
Claims
We claim:
1. A furnace including: a furnace lining and a frozen lining which
is positioned at least partly between the furnace lining and a
charge within the furnace; and control means to control the
operation of the furnace, the control means including means to
measure the temperature in a wall of the furnace adjacent the
frozen lining, means to estimate the thickness of the frozen lining
as a function of the temperature in the wall, and means to control
the rate of heat production in the furnace to urge a thickness of
the frozen lining towards a predetermined reference value.
2. A furnace according to claim 1, wherein the means to control the
rate of heat production in the furnace includes control over the
rate of addition of carbonaceous reductant to the furnace, so that
the rate of heat production is increased with an increase in the
rate of addition of carbonaceous reductant to the furnace to
thereby urge the thickness of the frozen lining to decrease, or the
rate of heat production is decreased with a decrease in the rate of
addition of carbonaceous reductant to the furnace to thereby urge
the thickness of the frozen lining to increase.
3. A furnace according to either one of claim 1, wherein the
control means further comprises one or more of the following
measurement means: means to measure furnace gas plant variables;
means to measure furnace cooling system variables; means to measure
furnace in-feed variables; means to measure furnace electrical
system variables; and means to measure furnace charge chemical
composition variables.
4. A furnace according to claim 1, which further comprises a
process for conducting error detection and validation of the
measurements, the process comprising analysis of the range of the
measurements and the rate of change of the measurements to validate
the measurements, and a process for replacing invalid measurements
with pre-recorded measurements according to a set of logical
rules.
5. A furnace according to claim 3, which further comprises means to
estimate the frozen lining thickness and hot face temperatures as a
function of the wall temperature measurements and gas plant
measurements.
6. A furnace according to claim 3, which further comprises means to
estimate heat losses in the furnace as a function of estimated
frozen lining thickness and hot face temperatures, the gas plant
measurements, and the cooling system measurements.
7. A furnace according to claim 1, which further comprises means to
measure sensible heat changes of spray cooled roof panels, spray
cooled off gas ducts, film cooled shell panels, air cooled hearth
panels, hot gasses and dust, and/or charge removed from the
furnace.
8. A furnace according to claim 7, which further comprises means to
estimate heat losses in the furnace as a function of the estimated
frozen lining thickness and hot face temperatures, the gas plant
measurements, the cooling system measurements, and measured
sensible heat changes.
9. A furnace according to claim 3, which further comprises means to
estimate a material balance of the furnace as a function of the
estimated frozen lining thickness and hot face temperatures, the
gas plant measurements, the in-feed measurements, the electrical
system measurements, and the furnace charge chemical composition
measurements.
10. A furnace according to claim 9, which further comprises means
to perform inventory control over the furnace using the material
balance of the furnace.
11. A furnace according to claim 9, which further comprises means
to estimate a future furnace charge chemical composition as a
function of the estimated frozen lining thickness and hot face
temperatures, the estimated heat losses, and the estimated material
balance.
12. A furnace according to claim 11, which further comprises means
to perform chemistry control of the furnace using the estimated
material balance, the estimated future furnace charge chemical
composition, the in-feed measurements, the electrical system
measurements, and the furnace charge chemical composition
measurements.
13. A furnace according to claim 6, which further includes means
for controlling start-up of the furnace to be performed using the
in-feed measurements, the electrical system measurements, the
furnace charge chemical composition measurements, and the estimated
heat losses.
14. A method for controlling a frozen interface in a furnace
between a furnace lining and a charge in the furnace, the method
comprising the steps of: (i) establishing the frozen lining; (ii)
measuring at least the temperature in a wall of the furnace
adjacent the frozen lining; (iii) estimating the thickness of the
frozen lining as a function of the temperature in the wall; and
(iv) controlling the rate of heat production in the furnace to urge
a thickness of the frozen lining towards a predetermined reference
value.
15. A method according to claim 14, wherein the step of measuring
at least temperature in the wall of the furnace comprises measuring
one or more of gas plant variables, furnace cooling system
variables, furnace in-feed variables, furnace electrical system
variables, and furnace charge chemical composition variables.
16. A method according to claim 14, which further comprises the
step of performing a process of error detection and validation on
the measurements, the process of error detection and validation
including the steps of: (v) analysing the range of the measurements
and the rate of change of the measurements; (vi) validating the
measurements; and (vii) replacing invalid measurements by
pre-recorded measurements according to a set of logical rules.
17. A method according to claim 14, wherein the thickness of the
frozen lining is estimated as a function of the temperature in the
wall and the furnace gas plant measurements.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to application no. ZA
2001/1817, the entire contents of which is expressly incorporated
herein by reference thereto.
FIELD OF THE INVENTION
[0002] The present invention relates to a furnace and a method of
controlling a furnace.
BACKGROUND OF THE INVENTION
[0003] THIS invention relates to a furnace that can be used for the
production of a metal value from a metal value bearing material and
specifically to such a furnace where the refractory lining is
protected by a frozen lining.
[0004] In processes for the production of metals from metal bearing
ores, furnaces frequently form an indispensable part of the
process. The ore is subjected to heat and certain reagents to
unlock the metal contained therein and to transform it to a form
from where it can be worked further.
[0005] Because of the high heat necessary for most processes and
the need to contain the heat energy and the charge, furnaces almost
always need an insulating lining known as a refractory lining.
[0006] Refractory linings form a high cost component in the
production process due to their specialised nature, and the
downtime needed to install a refractory lining also contributes to
the cost factor.
[0007] There is therefore a need to maintain a refractory lining
for as long as possible. Refractory linings wear away by a number
of different mechanism including mechanical thermal and chemical
wear.
[0008] Mechanical wear occurs through abrasion of charged material
against the refractory lining material, such as may occur during
charging of a furnace with hard material.
[0009] Thermal wear occurs when the temperature of the refractory
lining material rises above a certain refractory-specific safe
limit. Above such a temperature, the refractory lining material
loses its strength and may start to dissolve into the charge.
[0010] Chemical wear occurs when the refractory lining is exposed
to chemical compositions that tend to remove certain elements of
compounds from the refractory lining material, thereby weakening
its structure. This frequently occurs through what is commonly
known as a slag-attack, where a layer of slag on top of a charge of
liquid steel will attack the refractory lining material of a
steel-making furnace.
[0011] One way of preventing or reducing refractory lining wear is
by establishing and maintaining a layer of frozen charge between
the charge and the refractory to serve as a barrier against
mechanical, thermal and chemical wear.
SUMMARY OF THE INVENTION
[0012] In accordance with this invention there is provided for a
furnace having a furnace lining and a charge therein to have a
frozen lining at least partly between the furnace lining and the
charge, and for means to control the operation of the furnace, the
control means including means to measure the temperature in a wall
of the furnace adjacent the frozen lining, and means to estimate
the thickness of the frozen lining as a function of the temperature
in the wall and means to control the rate of heat production in the
furnace to urge a thickness of the frozen lining towards a
predetermined reference value.
[0013] There is also provided for the means to control the rate of
heat production in the furnace to include control over the rate of
addition of carbonaceous reductant to the furnace, for the rate of
heat production to increase with an increase in the rate of
addition of carbonaceous reductant to the furnace to thereby urge
the thickness of the frozen lining to decrease; or for the rate of
heat production to decrease with a decrease in the rate of addition
of carbonaceous reductant to the furnace to thereby urge thickness
of the frozen lining to increase.
[0014] There is also provided for the control means to include
means to measure furnace gas plant variables means to measure
furnace cooling system variables, means to measure furnace in-feed
variables, means to measure furnace electrical system variables,
and means to measure furnace charge chemical composition
variables.
[0015] There is also provided for a process of error detection and
validation to be conducted on the measurements, for the process of
error detection and validation to include analysis of the range of
the measurements and the rate of change of the measurements to
validate the measurements, and for invalid measurements to be
replaced by pre-recorded measurements according to a set of logical
rules.
[0016] The invention further provides for means to estimate the
frozen lining thickness and hot face temperature as a function of
the wall temperature measurements and gas plant measurements.
[0017] There is also provided for means to estimate heat losses in
the furnace as a function of estimated frozen lining thickness and
hot face temperatures, the gas plant measurements, and the cooling
system measurements.
[0018] There is also provided for means to measure sensible heat
changes of spray cooled roof panels, spray cooled off gas ducts,
film cooled shell panels, air cooled hearth panels, hot gasses and
dust, and charge removed from the furnace.
[0019] There is also provided for means to estimate heat losses in
the furnace as a function of the estimated frozen lining thickness
and hot face temperatures, the gas plant measurements, the cooling
system measurements, and measured sensible heat changes.
[0020] The invention also provides for means to estimate a material
balance of the furnace as a function of the estimated frozen lining
thickness and hot face temperatures, the gas plant measurements,
the in-feed measurements, the electrical system measurements, and
the furnace charge chemical composition measurements.
[0021] There is further provided for means to perform inventory
control over the furnace using the material balance of the
furnace.
[0022] The invention further provides for means to estimate a
future furnace charge chemical composition as a function of the
estimated frozen lining thickness and hot face temperatures, the
estimated heat losses, and the estimated material balance.
[0023] There is also provided for means to perform chemistry
control of the furnace using the estimated material balance, the
estimated future furnace charge chemical composition, the in-feed
measurements, the electrical system measurements, and the furnace
charge chemical composition measurements.
[0024] The invention further provides for start-up control of the
furnace to be performed using the in-feed measurements, the
electrical system measurements, the furnace charge chemical
composition measurements, and the estimated heat losses.
[0025] The invention also provides a method for controlling a
frozen interface between a furnace lining and a charge in the
furnace, the method comprising the steps of:
[0026] (i) establishing the frozen lining;.
[0027] (ii) measuring at least the temperature in a wall of the
furnace adjacent the frozen lining;
[0028] (iii) estimating the thickness of the frozen lining as a
function of the temperature in the wall; and
[0029] (iv) controlling the rate of heat production in the furnace
to urge a thickness of the frozen lining towards a predetermined
reference value.
[0030] There is also provided for step (ii) of the method to
include measuring gas plant variables, furnace cooling system
variables, furnace in-feed variables, furnace electrical system
variables, and/or furnace charge chemical composition
variables.
[0031] The invention also provides for the method to include
performing a process of error detection and validation on the
measurements, the process of error detection and validation
including the steps of.
[0032] (v) analysing the range of the measurements and the rate of
change of the measurements;
[0033] (vi) validating the measurements; and
[0034] (vii) replacing invalid measurements by pre-recorded
measurements according to a set of logical rules.
[0035] The invention further provides for step (iii) of the method
to include a step of estimating the thickness of the frozen lining
as a function of the temperature in the wall and the furnace gas
plant measurements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 is a schematic representation of the logic of a
control process for a furnace according to the invention.
[0037] FIG. 2 is a schematic representation of the feed-back used
in the control process.
[0038] FIG. 3 is a schematic representation of the multi-use of
input information in the chemistry control.
DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS
[0039] A process control layout for a furnace (not shown) with a
refractory lining and a charge is generally depicted by reference
numeral 1 in FIG. 1. The furnace has a frozen lining (not shown)
between the refractory lining and the charge.
[0040] Instrument readings from the furnace include sidewall
thermocouple measurements (2), gas plant instrument measurements
(3), cooling system instrument measurements (4), and in-feed,
electrical system and charge chemical composition measurements
(5).
[0041] A process of error detection and validation (6) is conducted
on the instrument measurements. The process includes analysis of
the range of the measurements and the rate of change of the
measurements to validate the measurements, the replacement of
invalid measurements by prerecorded measurements according to a set
of logical rules.
[0042] Once the measurements have been validated, or if invalid,
replaced by substitute values, the measurements are utilised for
the control of the process.
[0043] The frozen lining thickness and hot face temperatures are
estimated (7) as a function of the sidewall thermocouple
measurements (2) and gas plant instrument measurements (3). The
estimated frozen lining thickness and hot face temperatures (7) are
used to control the frozen lining thickness (11).
[0044] The heat losses in the furnace is estimated (8) as a
function of the estimated frozen lining thickness and hot face
temperatures (7), the gas plant measurements (3), and the cooling
system measurements (4).
[0045] The sensible heat changes of spray cooled roof panels (not
shown), spray cooled off gas ducts (not shown), film cooled shell
panels (not shown), air cooled hearth panels (not shown), hot
gasses and dust (not shown), and charge removed from the furnace
(not shown) is also measured and used in the determination of the
heat losses in the furnace (8).
[0046] A material balance of the furnace (not shown) is determined
and is used in the inventory control (9) of the furnace. The
material balance (not shown) is determined as a function of the
estimated frozen lining thickness and hot face temperatures (7),
the gas plant measurements (3), the in-feed measurements,
electrical system measurements, and furnace charge chemical
composition measurements (5).
[0047] The future furnace charge chemical composition (10) is
estimated as a function of the estimated frozen lining thickness
and hot face temperatures (7), the estimated heat losses (8), and
the estimated material balance (not shown). The estimated future
furnace charge chemical composition (10), together with the
estimated material balance (not shown), the in-feed measurements,
electrical system measurements, and furnace charge chemical
composition measurements (5) are used to perform chemistry control
over the furnace (12).
[0048] Start-up control over the furnace (13) is performed using
the in-feed measurements, the electrical system measurements, the
furnace charge chemical composition measurements (5) and the
estimated heat losses (8).
Ilmenite Smelting Furnace
[0049] The process control as described above is used for the
control of an ilmenite smelting process in a DC arc furnace.
Ilmenite mineral sand is smelted using anthracite as a reductant in
the furnace. The furnace is refractory lined with magnesite bricks.
Cold ilmenite, preheated ilmenite and anthracite are fed into the
furnace through a hollow electrode. High titania slag and metallic
iron are periodically tapped from the furnace. Hot gas containing
dust is removed from the furnace through a single off gas duct
where it is subsequently cleaned in a gas scrubbing plant. A film
of flowing water cools the furnace shell. The roof panels and off
gas panels are spray cooled and the hearth of the furnace is
air-cooled.
[0050] The furnace frozen lining and chemistry are controlled by
the amount of energy and carbon reductant input.
Gross Error Detection and Validation
[0051] Plant instruments can fall or drift, thereby giving invalid
or inaccurate readings. This would make any calculation or model
useless. For this reason, all raw data readings used by the control
system go through an error detection and data validation process.
The quality of the readings is marked as either good or bad. The
model components are marked as either enabled or disabled based, on
the status of their input tags. In the gross error detection, the
range of the reading and its rate of change are checked for
abnormalities. The data is validated by either a set of logical
rules or neural network models, where the important data that is
bad for some reason can be reconstructed if necessary.
Temperature Profiles and Frozen Lining Thickness Estimations
[0052] Dual sidewall thermocouples are used to read the temperature
of the sidewalls. Together with knowledge of the thermal
conductivity of the frozen lining and the refractory lining, an
internal node calculation is performed to determine the temperature
at any point between a sidewall thermocouple and the hot face,
which is the interface between the refractory and frozen lining.
This information is used to calculate the hot face temperature and
frozen lining thickness.
[0053] The value of the frozen lining thickness is used in the
frozen lining thickness control. This value is of more use in the
frozen lining control than just the thermocouple readings, because
it takes non-steady state conditions and time lapses between
thermocouple readings and the frozen lining thickness into
account.
Inventory Control
[0054] The total amount of material, including the dust losses, and
power added to the furnace between taps is determined for use in
inventory control, The analyses of certain elements in the feed
materials, slag and iron are used in the material balance to
determine the relative amounts of slag and iron produced The amount
of frozen slag is taken into account via the frozen lining
thickness calculation. Bath heights are calculated through the
relationship between mass and volume. The relative amounts of slag
and iron to be tapped are then determined using the heights of the
tap holes as reference points. During the addition of electrodes,
sounding measurements are taken through a hollow electrode. The
actual measurements of the slag and iron bath heights are used to
"zero" the control process calculation on almost a daily basis.
Heat Loss Calculations
[0055] Heat lost through the cooling system and exiting streams
from the furnace is calculated by means of the sensible heat gain
or loss of the cooling medium and exiting stream. The spray cooled
roof panels, spray cooled off gas ducts, film cooled shelf panels,
air cooled hearth panels, hot gasses and dust, and charge removed
from the furnace are all used to take readings for the heat loss
calculations.
Chemistry Predictors
[0056] Neural network models with high correlation coefficients are
used to predict the current % TiO.sub.2 in the slag, % C in the
iron and % Fe.sub.2O.sub.3 in the ilmenite, as well as those
percentages 2 hours ahead. This data is used for feed forward
control in the material and energy balance of the decision support
module. The neural network models are extensive. There are
approximately 42 inputs to each of the iron and slag models and 6
to the ilmenite model. Inputs include the data derived from the
other modules (frozen lining thickness, inventory control, heat
loss). The models auto train as the plant conditions change.
Frozen Lining Control
[0057] The philosophy used in the control of the freeze lining is
that the frozen lining is viewed as an additional layer of
"bricks". As long as the frozen lining is maintained, the magnesite
bricks will remain intact and should not have to be replaced for
many years. The maintenance of even and uniform frozen lining means
that the bath size is kept constant which makes for better
operational control. Tight control of the frozen lining thickness
is achieved by making regular changes to the C reductant addition
rates in both the positive (frozen lining getting thinner because
of an increased rate of heat production) and negative (frozen
lining getting thicker because of a decreased rate of heat
production) directions.
Chemistry Control
[0058] The reaction governing the process is given by:
FeTiO.sub.3+C+heat.fwdarw.Fe+TiO.sub.2+CO
[0059] The control objectives are to maintain the % TiO.sub.2 in
the slag of 86% with minimal deviation and to maintain the freeze
lining. This is achieved through manipulation of the C reductant
addition rate (AIR, anthracite to ilmenite ratio) and the energy by
input (IPR, ilmenite to power ratio). The system is interactive in
that both of the manipulated variables influence both of the
controller variables, as is shown in FIG. 3.
[0060] There are two portions to the control strategy, namely a
feed forward portion (ff) and a feed back portion (fb). The feed
forward portion attempts to absorb the disturbance introduced by
varying feed material composition (ilmenite and anthracite
analyses) and the feed back portion reacts on measurements of the
controlled variables (% TiO.sub.2 in slag and freeze lining
thickness).
[0061] Eff+Efb=Etot (IPR--specific energy, kg ilmenite per
(MWh)
[0062] Cff+Cfb=Ctot (AIR--specific carbon, kg anthracite per ton of
ilmenite)
[0063] The Eff portion is determined from a hard coded energy
balance and the Cff from a hard coded material balance.
[0064] The Efb and Cfb portions are equivalent to the changes that
were conventionally made by the shift supervisors based on the %
TiO.sub.2 in the slag as-tapped and the sidewall thermocouple
readings respectively. In the decision support system, these
portions are determined by a fuzzy logic rule set that was derived
from the experiences or operational staff and on line tuning.
[0065] The feed back portion consists of two loops, one fast and
the other slow, as is shown in FIG. 2.
[0066] The fast loop is run every 15 minutes and uses the estimated
frozen lining thickness. The slow loop is run after each tap and
uses the % TiO.sub.2 in the slag.
Start-up Module
[0067] During a furnace stoppage, the length of the stoppage and
energy lost is integrated. A given percentage of the lost energy is
then recovered through a specified power ramp, IPR and AIR
schedule. Once the start-up module is completed, the system
switches back to the chemistry and freeze lining control
modules.
[0068] The invention is not limited to the precise constructional
details as herein described.
[0069] The applicant believes that the invention is advantageous in
that it provides a furnace with means to control a frozen lining in
the furnace, wherein the bath size is kept constant for better
operational control and the wear on the refractory lining is
reduced.
* * * * *